Angular and linear absolute position sensors are widely used in automatic control systems as feedback-sensing devices in one or more control loops of the system. In the automotive industry, such position information may be used in substitution of more traditional, conventional control feedback provided by mechanical linkages, such as cables, rods, and the like.
For example, in the automotive field, it may be desirable to know the linear absolute position of a long travel mechanism, such as a rack and pinion mechanism (i.e., that moves when a driver of an automotive vehicle turns the steering wheel), or the position of a sliding door on a minivan. In the first example, a linear absolute position sensor can provide information as to the linear position of the rack and pinion mechanism, which corresponds to the orientation of the front wheels (i.e., the steering wheels) of the automotive vehicle. In the second example, it may be desirable to know exactly where the sliding door is positioned within the long travel between a completely closed position and a completely open position. There are many other examples in and outside of the automotive industry where a linear absolute position or a rotary (angular) absolute position is detected and used.
One approach to implementing non-contacting rotary and linear absolute position sensors is magnet-based and uses flux concentrators. In this conventional approach, it is known to also use Hall Effect sensing technology. The flux concentrators are used to increase measurement angles in rotary position sensors, increase the measurement range in linear travel sensors, and/or improve linearity of the magnetic response. One drawback, however, to this conventional approach results from the magnetic hysteresis associated with the flux concentrators. In particular, in view of conventionally used geometries for flux concentrators, the magnetic flux flowing through the concentrators changes with travel, and the sensor incurs an error (non-linearity) from the concentrator's magnetic hysteresis. As a result, flux concentrators of conventional design may require very accurate dimensioning and positioning.
U.S. Patent Application Publication No. 2004/0164727 A1 entitled “SINGLE MAGNET LINEAR POSITION SENSOR” discloses a sensor assembly for measuring linear position that includes a ferromagnetic flux concentrator, a magnet, and a galvanomagnetic sensing element such as a Hall Effect or magnetoresistive sensor.
In view of the foregoing, there is a need to provide a non-contact position sensor for rotary or linear travel that minimizes or eliminates one or more of the shortcomings referred to above.